1. Technical Field
This specification generally describes an apparatus for image forming, and more particularly describes an apparatus for image forming capable of effectively developing images.
2. Discussion of the Background
There is a widely known image forming apparatus having a developing unit including two conveyance screws and a development roller disposed above one of the two conveyance screws.
FIG. 1 is a cross-sectional view of a background developing unit 5 used in a background image forming apparatus. The developing unit 5 includes a first screw 55, a second screw 56, and a development roller 51 disposed above the first screw 55. FIG. 2 is a perspective view of the first screw 55 and the second screw 56. FIG. 3 illustrates another aspect of the background developing unit 5 of FIG. 1.
Referring to FIG. 1, the developing unit 5 further includes a developer-containing portion divided by a partition into a first chamber 53 and a second chamber 54. The first chamber 53 is provided with the first screw 55, and the second chamber 54 is provided with the second screw 56. Developer dispensed into the second chamber 54 from above may be agitated and conveyed by the second screw 56 to the first chamber 53. Part of the developer in the first chamber 53 is to be picked up by the development roller 51.
Referring to FIG. 2, the first screw 55 and the second screw 56 have a substantially equal shape, volume, and conveying speed. That is, the first screw 55 and the second screw 56 convey a substantially equal amount of developer per time unit. The first chamber 53 and second chamber 54 have a substantially equal volume. Therefore, a surface of the developer in the first chamber 53 and a surface of the developer in the second chamber 54 may be at a substantially equal height.
As illustrated in FIG. 1, when the first chamber 55 is filled with the developer, the second chamber 54 is also filled with the developer. When the second screw 56 in the second chamber 54 is buried in the developer, an upper portion of the developer may not be sufficiently agitated by the second screw 56. In other words, the developer may not be sufficiently charged. Those skilled in the art may appreciate that the use of insufficiently charged toner for development may cause drawbacks such as background contamination and a toner spatter.
On the other hand, as illustrated in FIG. 3, when the second chamber 54 has a relatively low level of developer, the first chamber 53 also has a relatively low level of developer. When the first chamber 53 has a relatively low developer, the height of the surface of the developer may vary before and after movement of a blade portion of the first screw 55Y. As a result, an amount of the developer picked up by the development roller 51Y may be unstable, and an abnormal image referred to as a conveyance-screw-pitch irregularity may be caused. When any rotary member for conveying developer by rotation is used instead of the screws, there is a possibility that a similar kind of abnormal image is caused.